1. Field of the Invention
The present invention relates to a method for forming a semiconductor microstructure and a method for fabricating a resonance tunneling device. More particularly, the present invention relates to a method for forming a silicon (Si) microstructure on an SIMOX (separation by implanted oxygen) substrate by use of crystal anisotropic etching and a method for fabricating a resonance tunneling device having such a silicon microstructure.
2. Description of the Related Art
In recent years, quantization functional devices utilizing a quantum effect have been studied and developed. Among these quantization functional devices, a resonance tunnel diode utilizing a resonance tunnel effect has been proposed and studied. A method for fabricating such a resonance tunnel diode is disclosed in Japanese Laid-Open Patent Publication No. 7-312419, where an etching mask having two etching windows which are close to each other and parallel to the &lt;211&gt; direction is formed on a (110) SIMOX substrate, and a narrow Si microstructure is formed under the etching mask by controlling an Si etching amount by crystal anisotropic etching, to be used as a quantum well of a resonance tunnel diode.
The above conventional method for forming a semiconductor microstructure has the following problems. First, due to limitations of the present alignment technique or an error in the measurement of the orientation of a substrate, the direction where the etching windows extend and the &lt;211&gt; direction of the substrate may not be strictly parallel, but may be deviated from each other to some extent. When the etching mask has long etching windows for the formation of a long Si microstructure, the etching proceeds toward a direction parallel to the &lt;211&gt; direction, finally reaching an edge of the etching mask, and thus an Si microstructure cut halfway may be formed.
Secondly, in the conventional lithographic technique, the space between the etching windows cannot be made so narrow for the reason of the limitation of the light wavelength. A very narrow space between the etching windows is also difficult for other reasons. For example, if the space is very narrow, extremely high precision is required at the alignment in the subsequent lithographic step. A method employing electron beam drawing and the like has been proposed to overcome these problems. However, this method does not seem to be practical in consideration of the drawing cost and throughput. This method entails difficulty even when used for research.
Thirdly, in the conventional method for forming a semiconductor microstructure, though the width of the semiconductor microstructure is controlled by the etching amount, the etching amount is difficult to be monitored during etching.
Therefore, there is a strong need in the art for a method for fabricating a semiconductor microstructure and a resonance tunneling device which overcomes the above-mentioned problems associated with conventional methods.